For many years there has been an established medical technique of controlling the growth of cancer tissue by implanting in that tissue chemical particles (or seeds) of radioactive material that produces radiation which is toxic to cancer tissue. Various chemical isotopes can be employed which have different radiation intensities, and, therefore, different lengths of time over which the radiation occurs before the activity expires. Many of the problems of this medical technique have been solved, but there has remained the problem of how to deliver the seeds to the proper location in the body with precision. It is an object of this invention to provide such a precise delivery instrument. It is another object of this invention to provide an instrument which, for the most part, can be used again and again, by being sterilized after each use, and yet with some parts that may be disposable after a single use. Still other objects will become apparent from the more detailed description which follows.